The present invention relates to a multi-purpose mobile cordless phone system, including means to allow a cordless phone to selectively communicate either via a local base station of a cellular phone network or via a local-loop connection of a fixed telephone network.
Throughout the following description and claims, the words “mobile phone” and “cordless phone” are used as generic terms for any compact portable device (for example, handheld phones, wrist phones, wearable phones incorporated into clothing) suitable for personal communication of voice/sound, data and/or visual image signals via a radio link.
It is well known that both mobile and cordless phones communicate via radio links, the former with a cellular phone network and the latter with a fixed telephone network. Given a typical cordless phone is used inside and within the close vicinity of a building, it has an adequate operational range measured in tens of meters, with a normal maximum outdoor range of 100-300 meters. On the other hand, a mobile phone may be used anywhere within any cell of a cellular network and thus needs to have an operational range of up to several kilometers. It is also known that the transmission power required for radio signals approximately follows the Inverse Square Law and thus the power output of a cordless phone is typically a few percent of the maximum power output of a mobile phone.
Due to the relatively high power output of mobile phones and their frequent close proximity to the body when being used, particularly during voice communication, various concerns have been expressed by others alleging potentially adverse health effects due to the use of mobile phones. As a result, it has previously been proposed that means be provided to allow a low-power cordless handset to communicate with a local base station of a cellular network via a high-power mobile transponder unit. For example, Bucalo et al (U.S. Pat. No. 5,444,778) proposed the transponder unit be incorporated within a briefcase. In fact, there are various other low radiation options available to the user for storage of the mobile transponder unit: for example, in a hand/shoulder bag, in a loose fitting jacket pocket, or, even located on a belt clip (if the transponder unit incorporates a suitable personal radiation shield).
Although the prior art communication system has the potential to overcome possible health concerns of the user, the necessary components represent a significant cost increase when compared to a stand-alone mobile phone, given it is necessary to provide the user with a cordless phone handset plus a mobile transponder unit. In view of this, the described prior art system has so far not been made available on a commercial basis.
Grant (GB 2340691) describes conventional cordless phone technology being used for communication between the cordless phone handset and the transponder unit, the cordless phone handset alternatively communicating with a fixed telephone network if a cordless phone base station is included within the system. However, in the system proposed by Grant, the handset (and/or transponder unit) and the base station form the components of a conventional cordless phone system. In other words, the base station has to incorporate a radio transceiver for communication with the handset (in addition to a suitable fixed telephone network interface).